This invention relates to a two axis gyroscope. Vibrating structure gyroscopes may be fabricated using a variety of different structures as the resonant element. These include beams, tuning forks, cylinders, hemispherical shells and rings. Successful commercial exploitation is dependent upon optimising the device performance while minimising the cost. An additional goal for some applications is reducing the size of the device.
Some conventional vibrating structure gyro designs are suitable for fabrication using modern micro-machining techniques. These may be constructed from bulk Silicon, polysilicon or electro-formed metal. These fabrication methods provide the capability of producing miniature gyros in high volume and at reduced cost.
Many applications for gyroscopic devices require rate sensitivity about at least two axes. Conventional vibrating structure gyros provide single axis rate sensitivity and therefore two devices are required which must be aligned along orthogonal axes. A vibrating structure gyroscope incorporating a resonator design which is inherently capable of sensing rate around two axes simultaneously would therefore be of great benefit. A single device would thus replace two conventional single axis units with obvious cost benefits. Also, the process of mounting and aligning the two single axis gyros would not be required.
There is thus a need for an improved vibrating structure gyroscope design capable of sensing rate about two axes simultaneously.
According to one aspect of the present invention there is provided a two axis gyroscope including a substantially planar vibratory resonator having a substantially ring or hoop-like shape structure with inner and outer peripheries extending around a common axis, carrier mode drive means for causing the resonator to vibrate in a Cosnxcex8 out-of-plane carrier mode, where n has an integer value of 2 or more, support means for flexibly supporting the resonator and for allowing the resonator to vibrate, in response to the carrier mode drive means, relative to the support means, carrier mode pick off means for sensing out-of-plane movements of the resonator, X axis response mode pick-off means for sensing in-plane Cosn1xcex8 response mode movement of the resonator in response to rotation of the gyroscope about the X axis where n1 has a value of n plus 1 or n minus 1, and Y axis response mode pick-off means for sensing in-plane Sin n1xcex8 response mode movement of the resonator in response to rotation of the gyroscope about the Y axis, where n1 has a value of n plus 1 or n minus 1, identical to that for the X axis response mode.
Preferably, the gyroscope includes X axis response mode drive means for nulling the X axis response mode movement of the resonator to permit the gyroscope to be operated in a forced feedback configuration.
Conveniently, the gyroscope includes Y axis response mode drive means for nulling the Y axis response mode movement of the resonator to permit the gyroscope to be operated in a forced feedback configuration.
Advantageously, the support means includes a plurality of flexible legs flexibly connecting the resonator to a support, with the number of legs being given by N equals 4n1 and with the angular separation between the legs being given by 360xc2x0 divided by N.
Preferably, the resonator is made from metal, quartz, polysilicon or bulk silicon.
Conveniently, the drive means and/or the pick-off means are electrostatic, electromagnetic, piezo or optical.
Advantageously, the carrier mode is a Cos2xcex8 out-of-plane mode, the X axis response mode is an in-plane Sinxcex8 mode, and the Y axis response mode is an in-plane Cosxcex8 mode, with the carrier mode drive means including two drive elements located at 0xc2x0 and 180xc2x0 with respect to a fixed reference axis in the plane of the resonator, with the carrier mode pick-off means including two pick-off elements located at 90xc2x0 and 270xc2x0 with respect to the fixed reference axis, with the X axis pick-off means including a pick-off element located at 0xc2x0 with respect to the fixed reference axis, with the Y axis pick-off means including a pick-off element located at 90xc2x0 with respect to the fixed reference axis, with the X axis drive means including a drive element located at 180xc2x0 with respect to the fixed reference axis and with the Y axis drive means including a drive element located at 270xc2x0 with respect to the fixed reference axis.
Preferably, the carrier mode is an out-of-plane Cos2xcex8 mode, the X axis response mode is an in-plane Sin3xcex8 mode, and the Y axis response mode is an in-plane Cos3xcex8 mode, with the carrier mode drive means including two drive elements located at 0xc2x0 and 180xc2x0 with respect to a fixed reference axis in the plane of the resonator, with the carrier mode pick-off means including two pick-off elements located at 90xc2x0 and 270xc2x0 with respect to the fixed reference axis, with the X axis pick-off means including three pick-off elements located at 0xc2x0, 120xc2x0 and 240xc2x0 with respect to the fixed reference axis, with the Y axis pick-off means including three pick-off elements located at 30xc2x0, 150xc2x0 and 270xc2x0 with respect to the fixed reference axis, with the X axis drive means including three drive elements located at 60, 180xc2x0 and 300xc2x0 with respect to the fixed reference axis and with the Y axis drive means including three drive elements located at 90xc2x0, 210xc2x0 and 330xc2x0 with respect to the fixed reference axis.
Conveniently, the carrier mode is an out-of-plane Cos3xcex8 mode, the X axis response mode is an in-plane Sin2xcex8 mode, and the Y axis response mode is an in-plane Cos2xcex8 mode, with the carrier mode drive means including three drive elements located at 0xc2x0, 120xc2x0 and 240xc2x0 with respect to the fixed reference axis in the plane of the resonator, with the carrier mode pick-off means including three pick-off elements located 60xc2x0, 180xc2x0 and 300xc2x0 with respect to the fixed reference axis, with the X axis pick-off means including two pick-off elements located at 0xc2x0 and 180xc2x0 with respect to the fixed reference axis, with the Y axis pick-off means including two pick-off elements located at 45xc2x0 and 225xc2x0 with respect to the fixed reference axis, with the X axis drive means including two drive elements located at 90xc2x0 and 270xc2x0 with respect to the fixed reference axis, and with the Y axis drive means including two drive elements located at 135xc2x0 and 315xc2x0 with respect to the fixed reference axis.
Advantageously, the carrier mode is an out-of-plane Cos3xcex8 mode, the X axis response mode is an in-plane Sin4xcex8 mode, and the Y axis response mode is an in-plane Cos4xcex8 mode, with the carrier mode drive means including three drive elements located at 0xc2x0, 120xc2x0 and 240xc2x0 with respect to the fixed reference axis in the plane of the resonator, with the carrier mode pick-off means including three pick-off elements located at 60xc2x0, 180xc2x0 and 300xc2x0 with respect to the fixed reference axis, with the X axis pick-off means including four pick-off elements located at 0xc2x0, 90xc2x0, 180xc2x0 and 270xc2x0 with respect to the fixed reference axis, with the Y axis pick-off means including four pick-off elements located at 22.5xc2x0, 112.5xc2x0 202.5xc2x0 and 292.5xc2x0 with respect to the fixed reference axis with the X axis drive means including four drive elements 45xc2x0, 135xc2x0, 225xc2x0 and 315xc2x0 with respect to the fixed reference axis, and with the Y axis drive means including four drive elements located at 67.5xc2x0, 157.5xc2x0, 247.5xc2x0 and 337.5xc2x0 with respect to the fixed reference axis.